Indicator papers preparation

Tests were made with indicator papers prepared from ordinary filter paper. In the following table is to be found the concen-... 

During operation, the pH-value of the scrubbing liquid must be checked with the aid ol indicator paper, for example it should be between 6.2 and 6.7. If this value increases, then either more water must be drained off and the supply of fresh water increased or special preparations such as phosphoric acids, mild, etc. must be added (Fig. 5). This process can be automated by the aid of a measuring device. 

When the liquid is coloured it is difficult to observe the change of colour of the indicator in such case, use is made of papers prepared by immersing filter-paper in a o-i% methyl orange solution and drying in an oven. 

In a 100-ml conical flask place 5.5 g (0.015 mol) of methyl 2,3,4,6-tetra-O-acetyl-/ -D-glucopyranoside (Expt 5.111), 50 ml of dry methanol and 10ml of a solution of sodium methoxide in methanol previously prepared by the cautious addition of 0.1 g of sodium to 20 ml of methanol. Stopper the flask and allow the solution to stand for 1 hour, then add sufficient ion exchange resin [Zeolite 225 (H )] to render the solution neutral to moist universal indicator paper. Remove the resin by filtration, wash with methanol and evaporate the combined filtrate and washings under reduced pressure (rotary evaporator). Triturate the colourless syrup with absolute ethanol to cause it to solidify and recrystallise from absolute ethanol. The pure methyl / -d-glucopyranoside has m.p. 108-109 °C, [oc]d° —30.2° (c2.8 in H20) the yield is 2.4 g (83%). 

Cognate preparations. Sebacic acid (decanedioic acid). Dissolve 40 g (0.25 mol) of methyl hydrogen adipate in 100 ml of absolute methanol to which 0.1 g of sodium has been added. Pass a current of about 2.0 amps until the pH of the solution is about 8 (c. 5 hours) test with narrow-range indicator paper. Transfer the contents of the electrolysis cell to a 500-ml round-bottomed flask, render neutral with a little acetic acid and distil off the methanol on a water bath. Dissolve the residue in 150 ml of ether, wash with three 50 ml portions of saturated sodium hydrogen carbonate solution, then with water, dry over magnesium sulphate and distil under reduced pressure. Collect the dimethyl sebacate at 155°C/8mmHg it melts at 26 °C and the yield is 14.6-16.0 g (51-56%). 

Add 1 drop of methyl violet indicator solution and introduce dilute HC1 or dilute NH3 solution (as necessary) dropwise and with constant stirring until the colour of the solution is yellow-green a blue-green colour is almost but not quite acid enough, yet it is acceptable for most analyses. (If the indicator paper is available, the thoroughly stirred solution should be spotted on fresh portions of the paper.) It is recommended that a comparison solution containing, say, 10 ml of 0-3m HC1 and 1 drop of indicator be freshly prepared this will facilitate the correct adjustment of the acidity. A more satisfactory standard is a buffer solution prepared by mixing 5 ml of m sodium acetate, 5 ml of 2m HC1, and 5 ml of water this has a pH of 0-5. 

Dimathyl-3-hydroxy-6-heptenoic acid. In a 500-mL flask, the crude ester prepared in Part A (37.00 g, 0.199 mol) is dissolved in a 2 N solution of potassium hydroxide (KOH) in methanol (130 mL, 0.260 mol). The solution is stirred at 25°C and disappearance of the starting material is monitored by GLC (Note 9). After 5 hr saponification is complete and the methanol is evaporated at reduced pressure (Note 11). The residue is taken up with water (500 mL), extracted with diethyl ether (3 x 100 mL), and the organic phase is discarded. The aqueous phase is acidified (pH 2.5 on universal pH indicator paper) with - 6 N hydrochloric acid (about 60 mL) and extracted with diethyl ether (5 x 100 mL). These latter ethereal extracts are washed with water (2 x 30 mL) and then with saturated sodium chloride (2 x 30 mL). The organic phase is dried over sodium sulfate, and filtered. Evaporation at reduced pressure affords crude 3,6-dimethyl-3-hydroxy-6-heptenoic acid as a viscous yellow oil that can be used in... 

Light microscopy can give a good impression of the drop size distribution, which is an important characteristic especially for indicating potential microbiological hazards in water-in-oil products (91). Avery simple test for judgment of the droplet size distribution in margarine is the use of dyed type of absorbent paper (indicator paper) specially prepared for such purpose (91, 92, 114). 

Some preparations (Procedures in Sections C, E, G, and J) require the synthesis of intermediates. Generally, pH must be controlled with a precision of about 0.3 units, and a good indicator paper can be used for this purpose. Some preparations (Sections C and G) require accurate pH readings on a calibrated pH meter. 

When determining sensitivity with alkali, the water used for diluting should be completely free from carbon dioxide. Otherwise too low a sensitivity is found. It is obvious from the above data that azolitmin paper prepared from 0.1 % indicator solution is the most sensitive reagent paper for strong acids and bases. The presence of 10 N hydrochloric acid and sodium hydroxide can be demonstrated readily with this paper. It is best also for weaker acids and bases. 

The concentration of indicator is important for other papers as well. The table at the end of this chapter gives, for a number of indicators, the concentrations best suited for the preparation of indicator papers. 

Haas has extended the procedure to include other indicators. He describes a method for preparing blue and red lacmoid papers to be used in the determination. A drop of unknown solution is placed on several strips of indicator paper. At the same time a series of comparison papers is made from buffer mixtures of known All the strips are then dried slowly over soda lime... 

It is even better to use the violet paper than either the red or blue litmus papers, for either an acid or alkaline reaction will be revealed. The aqueous solution of the purified litmus is treated with acid until the proper hue results, and the paper saturated with this solution. Other indicator papers are prepared from solutions of the pure indicators. 

B. Pratt and H. 0. Swartout have prepared indicator papers from fruit and vegetable extracts (cf. page 165) but mention no sensitivity limits. Filter paper was soaked in the aqueous extracts, dried, moistened with ammonium hydroxide, and again dried in air. The paper then has a neutral color. These natural indicator papers arc listed below. 

The third section of the book is devoted to the colorimetric pH determination. The chapter on preparation and properties of buffer solutions embraces the whole of the author s present knowledge of this field. The ninth chapter deals with the colorimetric determination of pH, in which connection the practical performance as well as the values of indicator constants are discussed at great length. The tenth chapter treats the very important subject of errors in the colorimetric method. Indicator papers are taken up in the final chapter. 

Procedure (a) Dilute a little amount of universal indicator solution with tap water, place the green solution in three small beakers (can be projected with an overhead projector). Drop hydrochloric acid into one of the beakers, in the other sodium hydroxide solution, in the third common salt solution. Place several drops of the solutions on strips of universal indicator paper, observe and compare the colors with the color chart, determine the pH values, (b) Fill a large beaker with tap water and add a few ml of phenolphthalein solution while stirring. Prepare a second beaker of the same size with a few drops of sodium hydroxide solution, a third beaker of the same size with a few drops of concentrated sulfuric acid. Pour the contents of the first beaker into the second one, the second one into the third beaker. 

If references cited in the text of the manuscript are omitted from the References section at the end of the paper, this indicates sloppy preparation of the manuscript. Examining some of the references is often useful to confirm the accuracy of the information reported. The reader of the journal would expect prior work to be accurately represented in the manuscript. 

There will be little or no synthetic details on the figures, except where they are really important. There will be very few indications of preparative yields however, it is worth emphasizing that all the reactions mentioned can be useful in practice. A selection of preparative methods forms an appendix. Nevertheless, a chemist planning synthesis of PCAs is advised to study original papers and the references therein carefully. 

Test for phenolic resins. The test material (dry) is heated in an ignition tube over a small flame. The mouth of the tube is covered with a filter paper, prepared by soaking it in an ethereal solution of 2,6-dibromoquinone-4-chloro-imide and then drying it in air. After the material has been pyrolyzed for about a minute, the paper is removed and moistened with 1-2 drops of dilute ammonia solution. A blue color indicates phenols (care must be taken with plastics that contain substances yielding phenols on pyrolysis, e.g., phenyl and cresyl phosphate, cross-linked epoxide resins, etc.). 

The presence of acrylonitrile in copolymers can also be demonstrated by heating a sample of the dry material in a test tube and testing with indicator paper for the formation of HCN. Prepare the indicator paper hy dissolving 0.3 g copper(ll) acetate in 100 ml water. Impregnate strips of filter paper, and then air-dry them. Just before use, dip the strips in a solution of 0.05 g benzidine in 100 ml 1IV acetic acid (prepared from equal parts of 2IV acetic acid and water). If HCN is formed and passes over the moist paper, the paper turns blue (Careful ). 

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